Beam’s eye view imaging for in-treatment delivered dose estimation in photon radiotherapy
Ross I. Berbeco in Beam’s Eye View Imaging in Radiation Oncology, 2017
Delivered dose verification based on rigid motion tracked in BEV images has also been studied for prostate cancer treatment. Azcona et al. (2014) studied a version of the shift-and-add technique in 2013. This study was performed using 32 prostate trajectories measured from eight patients. Prostate motion was measured by tracking the location of implanted fiducial markers with cine EPID. Unlike the previously described studies, these treatments were volumetric modulated arc therapy (VMAT) treatments. In intensity-modulated treatments, the anatomical motion is more difficult to track because the MLC leaves can obstruct large portions of the BEV image. Azcona et al. (2014) reported that at least one fiducial marker was visible, on average, 56.2% of the time (range 10.9%–90.2%). When no markers were visible, the prostate position was interpolated between the nearest images in which markers were detected. The visibility of markers or anatomical landmarks in BEV images for intensity-modulated treatments remains one of the main challenges in BEV-based delivered dose calculation for this treatment modality.
Proton Image Guidance *
Harald Paganetti in Proton Therapy Physics, 2018
Radiographic planar imaging is a viable technique for pretreatment localization if either bony anatomy or implanted fiducials are good indicators of the location of both target tissue and nearby critical structures. A cohort of prostate cancer patients received a planning CT and three follow-up CT scans to examine the constancy of the correlation between marker location and the surface of the prostate and seminal vesicles. While the prostate showed little deformation over the course of treatment, the position of the seminal vesicles was less correlated to the marker position [45]. In another study, patients with fiducial markers placed in their prostates received magnetic resonance imaging (MRI) scans at the time of their treatment planning CT and at a randomly assigned treatment fraction. The fiducial markers, prostate, bladder, and rectum, were contoured on each of the MRI images. It was found that fiducial marker location was not a good surrogate for the prostate surface in the anterior–posterior or craniocaudal directions [46]. Additionally, in some radiotherapy treatment sites, sparing of a nearby critical organ is at least as important as adequately treating the tumor volume, although fiducial markers are rarely placed in normal tissues, and so these organs are not visualized and localized relative to the high-dose regions of the treatment plan. Finally, fiducial marker placement could potentially seed tumor cells along the needle path [38], and marker placement in the lung has been shown to carry a high risk of pneumothorax [47]. For these reasons, direct volumetric imaging of soft tissues may be a preferable modality for pretreatment localization.
Imaging Science, Imaging Equipment (Pretreatment and On-treatment)
Mike Kirby, Kerrie-Anne Calder in On-treatment Verification Imaging, 2019
A fiducial marker is defined as something that could be used as a standard of reference or measurement—an object placed in the field of view of an imaging system that appears in the image produced, to act as a point of reference or measurement. For some clinical sites, it is possible to improve our geometric knowledge of the soft-tissue target structures by implanting fiducial markers within them since we cannot observe the soft-tissue structures themselves and/or they move differentially with respect to nearby bony structures. These markers are made of substances (usually metal) with a high contrast, with respect to the background tissues, for the energies of imaging involved. Usually stainless steel produces acceptable contrast for kV energy x-rays; gold is required for suitable contrast for imaging with MV energy x-rays (Mutanga et al. 2012). Recent research has proposed fiducials in a liquid/gel form (de Blanck et al 2018) that can be used in a number of clinical sites with suitably high-contrast imaging properties. The surrogates represent the position of the target volume structures within which they are implanted. Usually two or three markers are used so that acquiring images from any angle gives a unique image of their positioning. Assumptions are made that once implanted, they (a) do not migrate significantly with respect to the target tissue and (b) do not migrate significantly with respect to each other. Thus, any movement of the target tissue is reflected by movement of all the fiducial markers acting like a rigid body. They are used mainly for prostate treatments (see Figure 7.7) and also for some lung tumours. In a similar approach, surgical clips, placed postresection following, for example, lumpectomy in breast cancer patients, can be used for increasing visibility for partial breast irradiation of the surgical bed. Steel clips are easily visible for kV energy x-ray imaging.
Two-dimensional in vivo rectal dosimetry during high-dose-rate brachytherapy for cervical cancer: a phantom study
Published in Acta Oncologica, 2018
Eun Hee Jeang, Youngmoon Goh, Kwan Ho Cho, Soonki Min, Sang Hyoun Choi, Hojin Jeong, Kwanghyun Jo, Nuri Lee, Sanghyeon Song, Se Byeong Lee, Dongho Shin, Yeon-Joo Kim, Joo-Young Kim, Dae Yong Kim, Ui-Jung Hwang, Young Kyung Lim
Because the 2DD-ERB is equipped with two fiducial markers made of metal and the balloon can be filled with water, the 2DD-ERB is expected to be readily visible on radiography, CT, MRI, and ultrasonography, which are widely used for IGBT. Dose perturbation caused by the fiducial marker would be negligible since the marker was made of light metal and its volume was tiny (1.6 mm3). The 2DD-ERB can reduce the setup errors of applicators and, therefore, improve the consistency of the treatments. However, a certain amount of setup error with respect to the aligned 2DD-ERB may remain, which will be reflected in the dose distribution measured by the 2DD-ERB. Therefore, significant setup error is detectable by the 2DD-ERB. We found that the DARs decreased in an almost linear pattern to values below 1, with a drastic decrease from 1 to 0 within the narrow interval of 8–9 mm as the relative distance between the 2DD-ERB and the applicator set increased.
Image-guided hypofractionated double-scattering proton therapy in the management of centrally-located early-stage non-small cell lung cancer
Published in Acta Oncologica, 2020
Shivam M. Kharod, R. Charles Nichols, Randal H. Henderson, Christopher G. Morris, Dat C. Pham, Vandana K. Seeram, Lisa M. Jones, Maria Antonio-Miranda, Soon Huh, Zuofeng Li, Bradford S. Hoppe
All treatments were delivered at the University of Florida Proton Therapy Institute. Treatments were delivered on consecutive days, and all treatments were completed within 2–3 weeks. Daily image guidance was utilized with fiducial markers and double exposure of orthogonal kilovoltage imaging at the peaks of inspiration and expiration. Cone-beam CT (CBCT) was not utilized, as our radiation gantries were not equipped with CBCT capabilities. The fiducial marker volume, drawn at the time of simulation based on the MIP image, was expanded 2 mm (fiducial + 2mm) and superimposed on the daily kV imaging. Adjustments to patient positioning were made to ensure that on inspiration and expiration the markers fell within the fiducial + 2-mm volume. Patients also underwent verification CT scans on days 1, 2, 4, and 6 of treatment to confirm appropriate alignment. During the course of radiation therapy, patients were assessed by the treating physician weekly, and their toxicities were scored using the Common Terminology Criteria for Adverse Events, version 4.0 [10].
Fiducial markers and their impact on ablation outcome for patients treated with MR-guided transurethral ablation (TULSA): a retrospective technical analysis
Published in International Journal of Hyperthermia, 2021
Cameron Wright, Pietari Mäkelä, Mikael Anttinen, Teija Sainio, Peter J. Boström, Roberto Blanco Sequeiros
Screening transverse T2w, T1w, diffusion and thermometry images of the prostate were loaded separately into image processing software (Mango/UTHSCSA, San Antonio, TX). For each sequence, a trained radiologist (P.M.) contoured the artifact generated by the marker on each visible slice. Contouring was done in a random order to avoid any bias. The radiologist was also blinded to the patient number, sequence and implant type. Markers located outside the prostate were not considered. The volume, length and width of the susceptibility artifact was calculated for each marker. All marker types produced a characteristic hypointense void surrounded by a thin bright rim. The transition between the hypo- and hyper-intense region was designated as the edge of the artifact. Additionally, the size and orientation of markers was characterized relative to the main magnetic field, and the resulting influence on artifact size was measured. Supplemental Digital Content S2 demonstrates an example of fiducial marker segmentation on screening mpMRI.
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